Posted: 03/08/2017 at 08:37
How high is the raised bed? If it is only a couple of feet high, use breeze blocks at the fence. You won't need to mortar then, just lay them on top of each other offsetting the joins. They are heavy enough not to move if only 3 or 4 high.
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If the blocks aren't mortared they will definitely move once soil is built up against them. Breeze blocks are quite heavy but no match for the pressure the soil will apply to them.
Are the fence posts timber or concrete? If concrete you could use concrete gravel board stood against the posts. The weight of soil will hold them in place. That won't work with timber posts due to the spacing.